Microfluidics offers the precise control of many parameters of cellular micro-environments including fluid shear stress, diffusion of soluble factors, and patterning of cells and extracellular matrix. Microfluidic devices have been used to explore a variety of biological problems of interest, ranging from fundamental research in protein crystallization to diagnostic assays. As such, microfluidic devices are becoming a part of many new approaches to investigating cell behavior and interaction. On the micro-scale, certain physical phenomena and interactions play a much more significant role in system behavior when compared to the macro-scale. Developing new microchannel designs and methods will allow for more robust control of the micro-environment and system parameters leading to improved analysis.
As is known, cells do not live in isolation. In all multi-cellular organisms, such as the human body, the cells within the body continually receive and send signals that coordinate the growth, differentiation, and metabolism of the cells in diverse tissues and organs. For example, morphogens are signaling molecules secreted by cells. In embryos, concentration gradients of morphogens play a key role in the formation and differentiation of many tissues, as well as, set the stage for the formation of organs. Further, it has been found that more intricate structures are formed by local, and sometimes reciprocal, interactions between different cell types. For example, the hair follicle is formed and maintained according to reciprocal signaling between the epidermal and dermal components of the skin. Reciprocal interactions also take place in the nervous system during formation of axon scaffolds that are precursors to neuronal connections, as well as, in regeneration wherein glial signals can, in fact, be detrimental to the repair process. As such, it can be appreciated that a better understanding of tissue level signaling is important for the development of new therapies and for tissue engineering. In addition, robust tools for in vitro modeling may have utility for the discovery of new drugs that target signaling pathways.
To study reciprocal signaling in vitro, one can employ cells that either over-express a component of a pathway or have dominant negative allele. However, this process requires the prior knowledge (or at least a hint) of the pathways involved. Also, genetic manipulations are difficult if the interaction between the cells involves multiple pathways. Pharmacological inhibitors could be used, but these inhibitors are only available for some signaling cascades and tend to lack specificity.
An alternative way of studying reciprocal signaling is to observe two or more cell types involved as they are joined in co-culture or separated after having been in contact. Traditional co-culture techniques do not enable easy cessation of cell to cell communication within a co-culture. In a mixed co-culture, it is not possible to remove all signals originating with one cell type, while leaving the second cell type unaffected. For example, when using filter well inserts, cells are usually seeded on either side of a membrane. It can be appreciated that any effort to remove one cell type from a well is likely to disturb the other cell type. Even if one cell type is seeded on the bottom of a well and the other on a filter insert, it will be difficult and time consuming to remove the filter without causing crosstalk between the wells.
Further, it has been found that disparate cell types can be difficult to co-culture due to each cell types individual needs for stringent culture conditions. In addition, different cell types often develop and mature at different rates. As a result, roadblocks to the development of appropriate physiologically relevant connections between the cell types may be created if the cell types are initially cultured at the same point in time.
Therefore, it is a primary object and feature of the present invention to provide a microfluidic device and method for co-culturing cells in discrete channels of a microfluidic device.
It is a further object and feature of the present invention to provide a microfluidic device and a method for selectively coupling discrete channels of the device.
It is a still further object and feature of the present invention to provide a microfluidic device and a method that allows for cells to be simply and easily removed from a channel of a microfluidic device.
In accordance with the present invention, a microfluidic device is provided. The microfluidic device includes a first body having bottom surface and defining a channel. The channel includes an inlet and an outlet communicating with the bottom surface. A first fluid is provided within the channel of the first body. The first fluid has a radius of curvature at the outlet. The microfluidic device also includes a second body having an upper surface and defining a channel. The channel of the second body includes an inlet communicating with the upper surface and an outlet. A second fluid is provided within the channel of the second body. The second fluid has a radius of curvature at the inlet. The first and second bodies are movable between a first position wherein the outlet of the channel of the first body is spaced from the inlet of the channel of the second body and a second position wherein the fluid at the outlet of the channel of the first body communicates with the fluid at the inlet of the channel of the second body.
The first fluid has a surface tension at the outlet of the first body with the first and second bodies in the first position. The surface tension of the first fluid maintains the first fluid within the channel of the first body with the first and second bodies in the first position. The first body includes an upper surface and the inlet of the channel of the first body communicates with the upper surface of the first body. The fluid at the inlet of the channel in the first body has a radius of curvature less than the radius of curvature of the fluid at the outlet of the channel in the first body.
In accordance with a further aspect of the present invention, a method of co-culturing cells is provided. The method includes the step of providing a channel network in a first microfluidic device. The channel network includes a channel having an input and an output. The first channel is filled with a first media. A channel network is provided in a second microfluidic device. The channel network in the second microfluidic device includes a channel having an input and an output. The channel in second microfluidic device is filed with a second media. The first media at the output of the channel of the first microfluidic device is brought into contact with the second media at the input of the channel of the second microfluidic device.
The method may include the additional step of depositing a drop on the input of the channel of the first microfluidic device so as to generate the flow of the first media from the input of the channel of the first microfluidic device to the output of the channel of the first microfluidic device. The drop at the input of the channel of the first microfluidic device has a radius of curvature less than the radius of curvature of the first media at the output of the channel of the first microfluidic device. In addition, it is contemplated for the drop at the input of the channel of the first microfluidic device to have a radius of curvature less than the radius of curvature of the second media at the output of the channel of the second microfluidic device. The method may also include the step of disengaging the first media at the output of the channel of the first microfluidic device from the second media at the input of the channel of the second microfluidic device.
The first media includes a first set of cells and the second media includes a second set of cells. The interaction of the first and second sets of cells are observed after the step of bringing the first media in contact with the second media.
In accordance with a still further aspect of the present invention, a method of coupling a channel in a first body and a channel in a second body is provided. Each channel includes an input and an output. The method includes the steps of providing a drop at the output of the channel of the first body and providing a drop at the input of the channel of the second body. The drop at the output of the channel of the first body is brought into contact with the drop at the input of the channel of the second body.
The method may include the additional steps of filling the channel of the first body with a first media and filling the channel of the second body with a second media. A drop is deposited on the input of the channel of the first body so as to generate the flow of the first media from the input of the channel of the first body to the output of the channel of the first body. The drop on the input of the channel of the first body has a radius of curvature less than the radius of curvature of the first media at the output of the channel of the first body. In addition, the drop on the input of the channel of the first body may have a radius of curvature less than the radius of curvature of the second media at the output of the channel of the second body.
The drop at the output of the channel of the first body may be disengaged from the drop at the input of the channel of the second body. It is contemplated for the drop at the output of the channel of the first body to include a first set of cells and for the drop at the input of the channel of the second body to include a second set of cells. The interaction of the first and second sets of cells after the step of bringing the drop at the output of the channel of the first body into contact with the drop at the input of the channel of the second body is observed.